Depending on the results, the modifications can either be generalised or cancelled. Unlike web testing tools, this feature is based not on users but on the number of clicks.
Drafts and Experiments
Formerly known as ACE, Drafts & Experiments is an AdWords testing feature that aims at assessing the impact of modifying specific elements of a campaign, such as keywords, bids, landing pages... These edits are only displayed to a share of all users exposed to the campaign.